1. Field of the Invention
The present invention relates to polymers that are useful in photoresist compositions. More particularly, the present invention relates to polymers containing t-butyl cinnamate useful in photoresist compositions, which produce high resolution photoresist patterns with improved etch resistance.
2. Description of Related Art
Photoresist compositions containing copolymers of t-butyl acrylate or methacrylate, and hydroxy styrene monomers are known in the art.
The t-butyl acrylate moiety retards the alkaline solubility of the resist film in unexposed areas. In the exposed area, photogenerated acid and heat causes decomposition of the t-butyl ester group to a carboxylic acid, enhancing the alkaline solubility of the exposed area of the film. While some lithographic properties, such as shape of profile, linked to alkaline solubility improve as the amount of t-butyl acrylate is increased in the copolymer, other properties such as plasma-etch resistance suffer as the amount of hydroxy styrene is decreased.
Plasma etching is a well known method for producing microstructures on a substrate. Etching of the photoresist must be controlled and precise. Variables that must be considered during this process include power level, temperature, pressure, design, and etchant chemistry. The role of the photoresist also influences the etching process. For example, aromatic groups in a photoresist composition affects the etching stability and etch selectivity. That is, certain polymers in the photoresist composition affect the etch resistance, which is an indication of the etch selectivity. By manipulating the etch selectivity, control and precision of the etching process can be improved.
Accordingly, it is desireable to have a photoresist composition that provides desired shape and profile properties, while demonstrating improved etch resistance, i.e. etch selectivity.